POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
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<strong>BLAST</strong> X Thurs. Morning Session<br />
TWO REGULATORY PROTEINS CONTROL THE SWIM-OR-STICK SWITCH IN<br />
ROSEOBACTERS<br />
Robert Belas<br />
<strong>University</strong> <strong>of</strong> Maryland Biotechnology Institute, Center <strong>of</strong> Marine Biotechnology, 701 East Pratt<br />
St., Baltimore, MD 21202<br />
Members <strong>of</strong> the Roseobacter clade <strong>of</strong> α-Proteobacteria are among the most abundant<br />
and ecologically relevant marine bacteria. One <strong>of</strong> the most salient features <strong>of</strong> the roseobacters<br />
from aspects <strong>of</strong> marine ecology is their ability to enter into close physical and physiological<br />
relationships with “red tide” phytoplankton such as din<strong>of</strong>lagellates. For example, Silicibacter sp.<br />
TM1040, our model roseobacter, forms a symbiosis with the din<strong>of</strong>lagellate Pfiesteria piscicida,<br />
such that the din<strong>of</strong>lagellate cannot live without TM1040. Aiding TM1040 in development <strong>of</strong> the<br />
symbiosis is a biphasic swim-or-stick lifestyle wherein a genetic regulatory circuit controls<br />
whether the bacteria are motile and chemotactic or sessile and develop a bi<strong>of</strong>ilm. Bacterial<br />
swimming and chemotaxis behavior are initial, essential steps in establishment <strong>of</strong> the symbiosis.<br />
Once near the host surface, motility and flagellar synthesis are downregulated, while bi<strong>of</strong>ilm<br />
formation and synthesis <strong>of</strong> an antibiotic are upregulated. The abilities to swim using flagella and<br />
to form a bi<strong>of</strong>ilm via adhesins have been demonstrated to be important traits for both pathogenic<br />
and symbiotic bacteria. While it is generally agreed that motility and bi<strong>of</strong>ilm development are<br />
mutually exclusive, the molecular mechanisms that underlie the lifestyle switch remain virtually<br />
unknown for most bacterial species. We have used genetic screens to search for mutants<br />
defective in either the motile or the sessile phenotype, and have discovered many new genes<br />
including two previously unknown and novel regulatory proteins, FlaC and FlaD that are<br />
envisaged to act together with cyclic dimeric GMP to play important roles in the swim-or-stick<br />
switch. FlaC is predicted to function as a response regulator protein, with homology to a protein<br />
<strong>of</strong> Caulobacter crescentus known to be important for cell envelope function. FlaC - cells are<br />
skewed towards the motile phase, e.g., their populations have a greater percentage <strong>of</strong> motile<br />
cells and fewer rosettes, and have defects in antibiotic synthesis and bi<strong>of</strong>ilm formation. Thus,<br />
FlaC determines whether the switch is in the swim or stick position. FlaD is predicted to be a<br />
MarR-type DNA-binding protein. Mutations in flaD result in nonmotile cells that synthesize but<br />
cannot rotate their flagella, i.e., they produce paralyzed flagella. We hypothesize that FlaD is<br />
involved in the function <strong>of</strong> the flagellar motor, either by (1) acting directly to control transcription<br />
<strong>of</strong> the class IV fliL operon or (2) acting indirectly to control transcription or activity <strong>of</strong> a protein<br />
that acts as a ‘clutch’ to engage or disengage the flagellar motor. The implications <strong>of</strong> FlaC and<br />
FlaD activities in the swim-or-stick strategy and their impact on the symbiosis will be discussed.<br />
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